Generic injection devices are often used in ground milling machines to reduce the development of dust during the work process and/or to add fluid, in particular water, to the ground material to be processed in order to obtain desired properties. Typical ground milling machines that injection devices of this type are used in include, for example, cold milling machines for milling off road or ground surfaces, stabilizers for stabilizing ground of low bearing capacity and recyclers for repairing road pavements in need of repair. Ground milling machines usually comprise as a working device a milling drum with which the ground or the road can be milled and/or be thoroughly mixed. The milling drum is mounted directly or indirectly on a machine frame of the ground milling machine and extends with its rotational axis horizontally and transversely to the working direction of the ground milling machine. The milling drum is further usually mounted in a work chamber which is open towards the ground and in which the milling drum rotates in operation and comes into contact with the ground to be processed. The milling drum is usually shielded off towards the other sides, for example, by a protective hood or a milling drum box. As a result of the closed configuration of the work chamber, it is prevented, among other things, that the material milled off by the milling drum rotating about its longitudinal axis will be ejected in an uncontrollable manner into the ambient environment of the construction machine. The outwardly delimited work chamber is further used for the transport of material in order to enable the controlled removal of material milled off by the milling drum. In another application, the task of the work chamber is to provide a mixing space in which the milled raw material can be mixed with an additive in order to achieve fortification or stabilization of the ground, for example. Typical additives in this regard are hydraulic or bituminous bonding agents and/or water, for example.
In order to enable adding a fluid to the work chamber in working operation, the ground milling machine comprises an injection device. Specifically, the injection device usually comprises at least one fluid delivery device, by means of which the fluid can be introduced into the work chamber. Such a fluid delivery device can be a valve, for example, and comprise an outlet opening or an outlet nozzle opening into the work chamber. Frequently, the part of the fluid delivery device via which the fluid enters the work chamber is arranged in the interior of the work chamber. Hereinafter, the term ‘fluid delivery device’ shall comprise any means that are provided for direct delivery of the fluid into the work chamber through an outlet opening in a controlled manner. In contrast, an injection device comprises the constructional entirety for introducing a fluid into the work chamber and usually comprises at least two fluid delivery devices and, for example, a line system for supplying fluid to the fluid delivery devices. A generic fluid delivery device comprises inter alia a fluid supply chamber. In this instance, a fluid supply chamber means a space surrounded by walls into which chamber enters the fluid coming from a fluid supply and exits via an outlet opening from the fluid supply chamber into the work chamber. Specifically, the fluid supply chamber may, for example, be an individual chamber, an injection beam, a part of a ring line, etc. It is known to provide the outlet opening with a controllable closure, so that the outlet opening may be opened and closed in a valve-like manner, if required.
A typical application in which the introduction of a fluid into the work chamber of the ground milling machine is desired is the mixing of the material milled by the milling drum in the work chamber with water in order to achieve improved material properties of the ground material together with bonding agents such as lime, for example, which may have been previously applied to the ground to be processed. Alternatively or additionally, a reduction in the development of dust in working operation can be achieved by wetting the ground material. Further exemplary applications are the introduction of bituminous bonding agents, the production and introduction of foamed bitumen, etc.
A generic fluid delivery device for a ground milling machine is already known from DE 102 41 067 B3, comprising a fluid supply chamber with an outlet opening and a controllable closure device for the outlet opening. The closure device comprises an adjustable tappet which opens the outlet opening in a retracted open position and which closes the outlet opening in a closed position. For opening the outlet opening, the linearly adjustable tappet is retracted into the fluid supply chamber, so that the outlet opening is completely open in the open position. In contrast, for closing the outlet opening, the tappet is pushed into the outlet opening until it completely closes the cross-section of the outlet opening. In addition, a stroke movement of the tappet beyond the closed position is provided for cleaning the outlet opening or for removing dirt accumulated in front of the opening. To that end, the tappet can be pushed outward through the outlet opening beyond the closed position, the outlet opening remaining closed by the tappet. A displacement device is provided for displacing the tappet, by means of which the tappet can be displaced between the closed position and the open position. The displacement device is specifically a piston-cylinder unit.
However, in the closure device known from the prior art the outlet opening can only be opened completely or not at all, which is why the injection pattern can only be varied via the pressure in the fluid supply chamber and thus by means of the output amount. In many cases, this results in a non-uniform injection pattern, particularly when using multiple fluid delivery devices in one injection device, even to the point that the fluid drips out of the outlet opening in an uncontrolled manner in the case of low output amounts. Furthermore, the fluid delivery device is very large in the displacement direction of the tappet due to the required long overall stroke and therefore requires a comparatively large installation space.